Programming exercise 5.7: A Caesar cipher is a simple substitution cipher based on the idea of shifting each letter of the plaintext message a fixed number (called the key) of positions in the alphabet. For example, if the key value is 2, the word "Sourpuss" would be encoded as "Uqwtrwuu." The original message can be recovered by "reencoding" it using the negative of the key.

Write a program that can encode and decode Caesar ciphers. The input to the program will be a string of plaintext and the value of the key. The output will be an encoded message where each character in the original message is replaced by shift it key characters in the Unicode character set. For example, if ch is a character in the string and key is the amount to shift, the the character that replaces ch can be calculated as chr(ord(ch) + key).

NOTE: You do not have to check to ensure that characters are letters unless you want to. If you're more comfortable with Python and understand branching, this is fine. If not, simply encode the entire string AS GIVEN and this will be acceptable.